During the 3 year, the project will focus on secondary immune response in the middle ear. Antibody levels in middle ear washes and sera, cytologic response in middle ear washes, and histologic responses in middle ear mucosa will be assessed in animals previously sensitized with keyhole limpet hemocyanin (KLH). Both intradermal and intratympanic sensitization will be employed. Results will be compared with primary immune responses to KLH as determined during the 01 and 02 years of the project. In order to clarify the mechanisms of secondary immune response in the middle ear, subjects will be passively immunized and challenge responses assessed. Both antibody and T-lymphocyte passive sensitization will be employed. In addition to secondary immune response and passive sensitization experiments, our work on antibody subclasses in sera middle ear washes will continue.